We are interested in the post-transcriptional mechanisms by which E. coli controls the levels of specific proteins. We will study the structural features of mRNAs that can be accommodated by ribosomes during the initiation step. We will study the direct role of the initiator tRNA by asking if mutant tRNAs can replace the initiator. We will study the role during initiation of tRNAs reading the codon 3' to the initiation codon. We will study two translational repressors, one of which inspects several mRNAs in the initiation domain, apparently by directly recognizing primary sequences. We will study an E. coli mRNA that may bind to ribosomes using non-standard complementarity to 16S ribosomal RNA. We will probe the structure of the track within which mRNAs sit in the ribosome during initiation, using a new technology that should reveal all rRNA domains that surround the message.